1. Field of the Invention
The present invention relates to a packet transmission control apparatus, a mobile node, a control node, a packet communication method, and a packet communication system.
2. Related Background Art
Conventionally, a packet communication system has been put into practical use in which a packet is transmitted from a source node to a destination node through a plurality of routers. Among the plurality of routers existing on a pathway between the nodes, there may be a router having an unresolved media access control (MAC) address of a router to which the packet addressed to the destination node is to be routed (forwarded).
The router having the unresolved MAC address is a router among the routers through which a packet passes when transmitted to the destination node, and this router does not hold a MAC address of a successive routing destination of the packet.
The router having the unresolved MAC address for the successive routing destination (which will be tentatively referred to as the “router A”) needs to recognize the MAC address of the router which corresponds to the successive routing destination (which will be tentatively referred to as the “router B”) by the use of an address resolution protocol (ARP). In this event, the router A broadcasts an ARP request packet having an internet protocol (IP) address of the router B to a link to which the router B is connected. The broadcasted ARP request packet is received by all nodes on the link, and the contents of the ARP request packet are analyzed. Of the nodes on the link, the router B confirms that the router B itself is the object of the ARP request, and transmits to the router A an ARP response packet having the MAC address of the router B. Upon receipt of this ARP response, the router A obtains the MAC address of the router B.
The above-described operations by the router A will be referred to as the “MAC address resolution”. Meanwhile, a “time period necessary for resolving the MAC address” is a time period consumed from the time point at which the ARP request packet is transmitted by the router A until the router A receives and analyzes the ARP response packet and then obtains the MAC address of the router B.
If a plurality of packets addressed to the same transmittee reach the router having the unresolved MAC address at an interval within the time period necessary for resolving the MAC address (which is normally several milliseconds), there is a concern regarding the following problem.
Specifically, if the plurality of packets reach the router at a high frequency before the router resolves the MAC address upon receipt of the packets addressed to a destination host, the respective packets are replaced by the subsequent packets because a buffering area is limited. As a result, the packets except the one that reach the router last may be discarded. Discarding the packets in this manner may result in an occurrence of a packet receiving failure by the destination host (a packet loss).